Unit bearing electric motors are widely used for light to medium duty applications where quiet, efficient power is needed, as in fans or blowers for example. Such motors are usually of the induction type, and include a rotor assembly rotatably supported on a rotor shaft which is cantilevered from the frame of the motor stator. The rotor assembly typically includes a pair of rotor shaft bearings and a lubricant reservoir for providing permanent lubrication to the bearings to provide long service life for the motor with minimum maintenance. Commonly assigned U.S. Pat. No. 2,904,709, to Lautner, illustrates a unit bearing electric motor of this type.
Various arrangements are known for mounting the rotor assembly of a unit bearing motor onto the cantilevered rotor shaft of the motor. For instance, the above Lautner patent includes a generally cylindrical rotor housing within which the rotor bearings and lubricant reservoir are disposed. After the bearings and reservoir are inserted within the rotor housing, the assembly is mounted by advancing it axially of the rotor shaft of the motor until the free end of the shaft extends slightly beyond the end of the housing. A suitable retainer is affixed to the shaft for retaining the rotor assembly on the shaft, and the end of the rotor housing then closed by a suitable lubricant sealing cap. While this construction is straightforward, it will be appreciated that the various steps required in mounting and sealing the rotor assembly ultimately add to the manufacturing costs of the motor.
An arrangement which facilitates assembly of a unit bearing motor is illustrated in commonly assigned U.S. Pat. No. 3,663,849, to Heob. This patent illustrates an electric motor construction in which a retainer is assembled within the rotor housing of the rotor assembly of the motor. The rotor assembly may be assembled and sealed, and then mounted as a unit onto the rotor shaft of the motor so that the retainer cooperates with the rotor shaft for retention of the rotor assembly on the shaft. While this construction has proven very successful in minimizing manufacturing expenses of this type of motor, a fair amount of assembly is still required before the rotor assembly of the motor may be inserted as a unit onto the rotor shaft of the motor.
Since the expenses associated with assembly of unit bearing motors of the present type represent a significant percentage of the overall cost of the final product, any manner by which assembly may be facilitated helps to reduce the final cost of the product. Thus, a unit bearing electric motor construction and method of assembly which facilitates mounting of the motor rotor assembly on the rotor shaft helps to minimize the cost of the finished product.